It's hard to know exactly how it would run, but the Radeon 7850 should do reasonably well. For the money though, I would look for an Intel Haswell (or event Ivy Bridge) class CPU. The new AMD R9 270 GPUs are pretty cheap cards for the power they give and you could through that in one of the cheaper Dell XPSs.

Maybe there's someone still around here that has more experience with the AMD CPUs.